1. Field of the Invention
The present invention relates to a module for controlling a Light Emitting Diode (LED) current for selective feedback so as to control constant currents of LED channels, an apparatus and a method for driving LEDs using the same.
2. Description of the Related Art
In general, a liquid crystal display refers to a device which displays a desired image according to an amount of light transmitted on an upper substrate of being a surface on which the desired image is displayed, by controlling an intensity of an electric field formed at the liquid crystal layer to thereby modify a molecular order of a liquid crystal material after forming a liquid crystal layer with anisotropic permittivity between upper and lower substrates of being transparent insulating substrates.
Since the liquid crystal display is a non-emissive display device incapable of emitting light by itself, it needs a back light which is installed on a rear surface of a liquid crystal panel which displays an image so that all screens can be maintained at the same brightness level.
A Cold Cathode Fluorescent Lamp (CCFL) or an External Electrode Fluorescent Lamp (EEFL) has been used as a light source of a back light for a liquid crystal display. However, an LED lamp has recently been in the spotlight as a next-generation light source which has characteristics of superior effects than the CCFL or the EEFL in terms of energy reduction and semi-permanent use.
Until now, an LED has been mainly used just as a light source of a back light for a liquid crystal display, such as a mobile phone. However, as luminance of an LED has become improved, a use range of the LED is enlarged to include a light source of the back light for a large-sized liquid crystal display.
An apparatus for driving an LED in the prior art includes at least one LED driving unit for driving a plurality of LED channels, and at least one DC/DC converter.
In general, since an error generated during product's production causes a difference between forward voltages even if each of LED elements is designed to have the same forward voltage, a lower end voltage of the LED channel is feedback-received to thereby control an output voltage of the DC/DC converter so as to maintain constant luminance.
The DC/DC converter boosts a voltage inputted from a power source to transfer the resultant voltage to an LED channel so as to maintain luminance of the LED channel. At lower ends of a plurality of LED channels, a linear controller for controlling a current of each channel to be constant, and a feedback controller for feedback-receiving a lower end voltage or current of each channel may be included.
There is a limit in the number of LED channels and the number of the LED driving unit which may be driven based on performance of one DC/DC converter. In the case where the LED driving unit is manufactured in a module form, there is a limit in the number of connectable LED channels as well.
Therefore, when a back light unit is implemented by using a plurality of LEDs, the above-described limits result in restrictions on arrangement of a plurality of LEDs. In addition, LEDs may be connected to only a part of pins in the LED driving module since there is a limit in the number of the LEDs operable in one DC/DC converter, which results in connection inefficiency between the LEDs and the pins.